1. Field of the Invention
This invention relates generally to cardiac pacing leads, and more particularly to an apparatus and method for inserting such leads.
2. Discussion of the Prior Art
Cardiac pacemakers for treating bradycardia commonly employ pacing leads for connecting an electrical pulse generator to excitable cardiac tissue, usually within the heart's right ventricle. Such leads have one or more electrodes proximate the distal end thereof and also commonly employ tines located just distal of the tip electrode for holding that electrode in contact with endocardial tissue in the right ventricle. The tines engage the trabeculae, resisting movement of the lead tip due to body movement and/or contractions of the heart muscle itself.
More recently, researchers have found that cardiac stimulation can have a beneficial effect in treating patients suffering from congestive heart failure (CHF). By properly controlling the AV interval of the pacemaker, a sick heart may be made to pump more efficiently. Pacing therapy for the treatment of CHF, however, often requires the ability to stimulate the left ventricle, either alone or in conjunction with right ventricular stimulation. Current methods for achieving left ventricular pacing require placement of an epicardial lead, via thoracotomy or a thoracoscopic approach. Because of the usual poor condition of CHF patients, both of these procedures are "high risk" due to the trauma of the surgery itself and the need for general anesthesia. To obviate the need for a thoracotomy, left ventricular access (LVA) leads have been developed that may be introduced through the coronary sinus and then advanced through the coronary veins so that the lead's stimulating tip electrode can be positioned on the surface of the left ventricle near the apex of the heart.
In co-pending application (Ser. No. 08/788,647), assigned to the same assignee as the present invention, an over the wire lead design is disclosed. This particular application uses a guide catheter and guide wire for placing the lead in the coronary sinus and left sided coronary veins. This over the wire design, as with other conventional over the wire designs, requires that the guide wire pass through an inner lumen of the lead for the entire length of the lead, resulting in considerable drag as the lead is tracked over the wire. While lubricious coatings are used to reduce friction between the leading guide catheter, a significant amount of drag still exists.
Feeding an endocardial or intravenous lead along the desired predetermined path to implant the electrode or electrodes in a desired implantation site, either in a chamber of the heart or in the selected coronary vein, can be sometimes difficult. This is especially true for routing leads through the coronary sinus and into a branching vein on the left myocardium. The difficulties often are a result of anomalies in the vascular anatomy and the number of veins encountered when locating the desired path. Furthermore, the stylet and guide wire has to be rigid enough to afford pushability to the lead and to provide navigation to the lead so as to arrive at the desired location. However, because of the tortious anatomy, a stiff lead may cause damage to the coronary veins.
Therefore, what is needed is a LVA lead that has minimal friction between the lead and guide wire as the lead is positioned and which additionally has a suitable flexible distal section to improve tractability through the tortious anatomy and minimize risk of damage to coronary veins.